Solid ionic conductor materials find particular use as solid electrolytes in high temperature, high energy density storage batteries. The anode reactant in such batteries usually is sodium or lithium, and electrolyte materials that are capable of conducting alkali metal cations and of withstanding the harsh environment within the batteries are of particular interest as solid electrolytes.
The conduction of lithium ions in various borate glasses has been extensively studied; see for example Irion et al, J. Solid State Chem., 31. 285-294 (1980) where vitreous fast ionic conductors in the system B.sub.2 O.sub.3 -Li.sub.2 O-LiCl are described, Smedley and Angell, Mat. Res. Bull., 15 (4), 421-425 (1980) where conductivity measurements in the Li.sub.2 O-LiF-B.sub.2 O.sub.3 system are reported and U.S. Pat. No. 4,184,015 which describes an amorphous cationic conductor of lithium comprising a composition corresponding to the general formula (B.sub.2 O.sub.3,xM.yN).aLi.sub.2 O.bLi.sub.z Q where M is selected from Al.sub.2 O.sub.3, V.sub.2 O.sub.5, P.sub.2 O.sub.5, As.sub.2 O.sub.5 and As.sub.2 O.sub.3, N is selected from SiO.sub.2 and GeO.sub.2 and Q may be a halogen anion or other anions, exclusive of O.sup.2-.
U.S. Pat. No. 3,911,085 describes the preparation of crystalline lithium haloboracites of the formula Li.sub.4 B.sub.7 O.sub.12 X where X is Cl, Br, I or a mixture thereof which are useful as solid electrolytes for galvanic cells. The preferred lithium haloboracites are those in which X is a mixture of Br and Cl where Br is 20 to 50 mole percent of X.
The conduction of sodium or potassium ions in borate glasses has also been studied. Eichinger and Deublein, Mat. Res. Bull., 15, 1263-1266 (1980) describe sodium phosphateborate glasses which exhibit high ionic conductivities for sodium ions. After milling of these amorphous compounds, crystallization occurred and densified samples showed higher conductivities than the glassy samples. The ionic conductivity of the polycrystalline compound Na.sub.8 P.sub.4 B.sub.2 O.sub.17 at 300.degree. C. is between 10.sup.-1 and 10.sup.-2 ohm.sup.-1 cm.sup.-1 which compares favorably with .beta.-alumina, the most often used of all cationic conductors. However, being crystalline, these compounds suffer from the usual disadvantages associated with pressing and sintering of bodies.
U.S. Pat. No. 3,829,331 describes an amorphous glass system based on sodium borate which is said to demonstrate reasonably high sodium ion conductance. The compositions, which may contain halide additives to modify viscosity, expansion coefficient and the like, are said to have utility as the membrane material in alkali metal-sulfur batteries. U.S. Pat. No. 3,877,995 describes analogous amorphous glass systems based on potassium borate which are also said to have utility as the membrane material in alkali metal-sulfur batteries.